In accordance with technological developments, electronic devices such as mobile phones, home appliances, personal computers (PC), personal digital assistants (PDAs), liquid crystal displays (LCDs), and the like, have been changed from an analog scheme into a digital scheme, and electronic device speeds have increased due to an increase in an amount of data processed by the electronic devices.
Therefore, a universal serial bus (USB) 2.0, a USB 3.0, and a high-definition multimedia interface (HDMI) have widely been circulated as high speed signal transmitting interfaces, and have been used in many digital devices such as personal computers and digital high-definition televisions.
These high speed interfaces adopt a differential signal system transmitting differential signals (differential mode signals) using a pair of signal lines, unlike a single-end transmission system that has been generally used for a long period of time. However, the electronic devices that are digitized and have an increased speed are sensitive to a stimulus from the outside, such that distortion of signals due to high frequency noise has been often generated.
In order to remove this noise, a filter has been installed in electronic devices. For example, a common mode filter used as a coil component is used to remove common mode noise. Common mode noise is noise generated in the differential signal line, and the common mode filter removes the common mode noise that may not be removed by an existing filter. Accordingly, the common mode filter has been widely used in a high speed differential signal line, or the like.
In various coil products including the common mode filter, the numbers of coil turns and stacked coil layers are increased in order to obtain high inductance.
In this case, a via having a vertical structure and formed of a metal is required for interlayer connection of the coil layers. The via has a recessed structure, recessed to have a depth corresponding to a thickness of an insulating layer. When these vias are accumulated in the same position, a via non-plating defect may occur.